Controlling placement and minimizing distortion of images in an imaging device

ABSTRACT

What is disclosed is a novel system and method to control an imaging device. A first collection of a plurality of two-dimensional image points in a first vector space for a source image and a second collection of a plurality of two-dimensional image points in a second vector space for a target image are received. The first collection of two-dimensional image points and the second collection of two-dimensional image points are converted into a homogenous form to apply affine matrix transformations. A matrix transformation is solved to map the first collection of the plurality of two-dimensional image points to the second collection of the plurality of two-dimensional image points. The matrix transformation is used to adjust distortion of the target image in an imaging device.

TECHNICAL FIELD

The present invention is directed to systems and methods for controllingplacement and minimizing distortion of images by scanners, copiers, andprinters.

BACKGROUND

Generally, in a duplex printed sheet it is desirable and expected thatimages on each side of a page are aligned correctly on a page. A commontest is to print a test pattern on each side of a sheet such that withperfect alignment the registration marks will be aligned when the sheetis viewed is a see-thru fashion (typically, holding the sheet to a lightsource so that a customer can visually test alignment). There arenumerous reasons why registration may be poor, for example including butnot limited to image distortions or placement on sheet due to situationssuch as paper shrinkage due to the fusing step, mechanical misalignmentof the sheet in the paper path, or magnification errors caused by thexerographic process. Further, in situations where the sheet is fusedtwice and inverted for duplex, alignment and printable substrateshrinkage typically varies on a per sheet side basis. As such undesiredregistration errors are introduced by the inherent limitations andanomalies of the device. Registration of image-to-image, image-to-sheet,or sheet-to-device can be suboptimal for multiple reasons, includingpaper shrinkage and setup error caused by the operator or by devicelimitations. Poor show-through or see-through alignment and/or poorhighlight color (HLC) registration results in reduced Customersatisfaction.

Systems for control of image placement provided by conventionalmeasurements are typically limited. For example, in most conventionalsystems, only printer spatial errors at the corners of a sheet aredetermined. For most media, the measurement process is typicallyperformed manually. Errors that occur during printing or scanning can becaused by, for example, Raster Output Scanner (ROS) scan line bow, ROSmagnification, lateral errors, and skew errors, which cannot bedetermined from measurements taken using conventional techniques. Papershrinkage caused by the fusing process can also result in errors thathave well defined intra sheet signatures.

Existing registration methods typically use basic algebra/trigonometryand piece-wise mechanical and xerographic setup adjustments. Forexample, calculating rotation needed after a shift. Alignment in imagingcontexts is also common. Further, other 2D least squares techniquesordinarily use a complicated polynomial form (e.g., y=β₀+β₁x+β₂x²+β₃x³)or complex multivariate form (e.g., y=β₀+β₁u+β₂v+β₃u²+β₄uv+β₅v²) whichis incompatible or less well suited for commonly available imageprocessing systems/tools. See: Linear Algebra and its Applications, byDavid C. Lay, Addison Wesley, 3^(rd) Ed., (Jul. 18, 2002). ISBN-10:0201709708, ISBN-13: 978-0201709704, the teachings of which areincorporated herein by reference in its entirety.

Accordingly, what is needed in this art are systems and methods forcorrecting image-to-image, image-to-sheet and sheet-to-deviceregistration errors which overcome many of the above-identified problemswith existing registration techniques.

BRIEF SUMMARY

What is disclosed is a novel system and method for correctingimage-to-sheet and image-to-image registration errors which minimizesimage distortion in image capture devices (such as scanners) and inimage output devices (such as printers). The present system and methoddetermines an amount of a spatial error for a scanner or a printer byusing an ideal reference which, in one embodiment, is a referencetwo-dimensional array comprising a grid having a geometric shape whichis stored as dots, for example, on film or in a computer readable file.Positional information associated with the reference two-dimensionalarray is compared with an actual two-dimensional array substantiallysimilar in shape to the first grid to determine an amount of spatialerror. As there are multiple registration measurements throughout themedium, individual spatial errors in the scanner or printer, and theirunique error contributions can be determined. Once determined, imagesplaced for example, on a platen of a scanning device, can be manipulatedsuch that misregistration errors across differing devices can becompensated by sending along error mapping information with the imagedata.

The present method can be used to calibrate images with a grid ofcalibration points and measure the points after printing in eithersimplex or duplex mode. The present invention overcomes problems withexisting registration and error correction techniques by leveragingcomputer graphics and linear algebra mathematics (affine form,homogeneous coordinates) for correcting image-to-image, image-sheet andsheet-to-device registration errors. Unlike prior art solutions, themathematical corrections performed by the present invention are in CTMform and therefore readily consumable by e.g., Postscript, imageprocessing, and computer graphics cards, and can be decomposed intodiscrete operations. Further, the present method uses a common computergraphics paradigm applied to print registration. This form makes it easyto integrate into a decomposer or graphics accelerator that supportsmatrix operations (e.g., PostScript). For printing, the correctiontransformation pre-distorts the image such that, when the sheet isprinted, this distortion cancels the distortion introduced by theprinting process. Alternatively, for scanning the image is correctedpost-scanning but prior to subsequent processing.

Vectors spaces and mapping between vector spaces are used along withlinear algebra for matrix algebra, inverse mappings, and pseudo-inverse.Matrix algebra is utilized herein to solve for an amount of aregistration correction transformation using a pseudo-inverse. Adisplacement vector magnitude for each point is calculated and thecollection of all displacements is used to characterize the error (e.g.,Mean, SD, Max, Min). An optimized linear solution is derived. Thepresent method also creates a transformation that simultaneously andefficiently addresses scaling, rotation, translation, and shear as partof the composite transformation matrix (CTM) produced. Overlapping pointgraphics are used to show see-through alignment for current/actual andcorrected states. Use of vector flow graphs of displacement vectors isuseful as a visual aid in understanding of registration errors andassessing degree of linearity of data or verifying “goodness of fit”.Appropriately generated, these graphs are useful in terms of operationsand demonstration of ability to correct for system errors. Moreinformation on “goodness of fit” and vector flow graphs is described inU.S. patent application Ser. No. 12/194,958, (Attorney docket number20071485-US-NP filed Aug. 20, 2008, entitled “Method To Improve Image onPaper Registration Measurements” by Kulkarni et al., and commonlyassigned herewith to Xerox Corporation and the teachings of which isincorporated herein by reference in its entirety.

In one embodiment, a calibration image or reference image with a grid ofpoints in known coordinates is first printed. Actual points displaced bythe printing process are measured. A mathematical mapping betweenreference and actual is made for each side of interest. The affinetransformation produced is in computer graphics composite transformationmatrix (CTM) form. Mappings may also be made either directly orindirectly between actual data for both see-through and highlight color(HLC) registration. Calibration and measured coordinates are convertedinto homogeneous coordinates or to homogeneous form. In one embodiment,a pseudo-inverse is applied to create a least squares inverse ofcalibration points. Matrix algebra is used to solve for thetransformation and for mapping between calibration and actual spaces.The inverse mapping provides a correction transformation from actual tocalibration that will be applied to the image prior to printing. Othersimilar mappings are used for image-to-image alignment.

In another embodiment, the present method corrects for see-throughregistration error in imaging devices. In the case when see-through (orshow-through) points printed on each side of a duplex sheet areperfectly aligned there is zero displacement. A reference image with agrid of points that span the document is used. Registration error is thedifference between actual measured points and the reference. Images maybe see-through aligned but not aligned to reference. Conversely, eachside may be aligned to reference, which indirectly gives goodsee-through alignment and a more accurate presentation. Image-on-imageregistration is considered for both see-through alignment and highlightcolor (HLC) image alignment to a single side.

Unlike the prior art, the present method provides mathematicalcorrections for image-to-image mapping. Corrections to better than 0.1mm mean displacement error have been shown. The ability to realize thismathematical correction is only limited by the inherent variabilitywithin a particular imaging device. Further, the mathematicalcorrections performed hereby are readily consumable by e.g., Postscript,image processing, and graphics cards, and can be decomposed. Further,insights into variability may be gained that could lead to reductions invariability by examining the decomposed mathematical corrections taughtin the present invention.

Many features and advantages of the above-described method will becomereadily apparent from the following detailed description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the subject matterdisclosed herein will be made apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a general mapping or transformation K of a collectionof coordinate points P₀ to a collection of target points P₁;

FIGS. 2-3 illustrate two-dimensional arrays as actual and referenceimage data points used for image registrations;

FIG. 4 illustrates an example of using a scanner to capture actual andreference image points used for image registrations;

FIGS. 5-8 illustrate spatial errors and corrections to an actual imageback to reference images;

FIGS. 9-11 illustrate spatial errors and corrections to an actual imageback to an actual image used in image registrations;

FIG. 12 illustrates spatial errors and corrections to a printed formused in image registrations;

FIG. 13 is a chart of various embodiments for forward mapping andinverse mapping of a collection of source points P₀ to a collection oftarget points P₁;

FIG. 14 is a flow diagram for correcting the errors in FIGS. 5-13according to an embodiment of the present invention;

FIG. 15 is a system diagram of the used to carry out the flow of claim14, according to an embodiment of the present invention; and

FIGS. 16-24 are a series of histogram plots computed by a mathematicalmodel of the flow of FIG. 14 on the system of FIG. 15, according to anembodiment of the present invention.

DETAILED DESCRIPTION

What is disclosed is a novel system and method for computing andcontrolling the precise placement and minimizing the distortion ofimages in image capture devices (such as scanners) and image outputdevices (such as printers). Various embodiments hereof control both theremoval of distortion as well as the precise placement of images inimage capture devices and imaging forming devices. The present method isintended to work for both simplex and duplex alignment and registration.

Mathematical Notations

A coordinate point p is defined by its {x,y} values in a 2D vector spaceV. For multiple points each individual point can be defined asp_(n)={x_(n),y_(n)}. A collection or set of points P={p₀, p₁, p₂, . . ., p_(n)}. Coordinate points are relative to a particular vector space.For set P relative to vector space V, this is denoted as [P]_(v). Thepresent invention involves mapping of a collection of points from onespace to another space. The mapping is a function or transformationbetween vector spaces. The first space is commonly referred to as thedomain; the second space is commonly referred to as the co-domain. Moresimply, this will be referred to as the source vector space S, and thetarget vector space T. The mapping or transformation of points shall bereferred to as K, such that we define a mapping as K: S→T. Morespecifically, since coordinate points are defined relative to a givenvector space, we may define the mapping of a collection of points fromone space to another as: K: [P₀]_(S)→[P₁]_(T) where P₀ is the originalpoint set and P₁ represents the transformed point set. In words, acollection of coordinate points P₀ in vector space S is mapped to a newcollection of coordinate points P₁ in target vector space T via amapping or transformation K. This is shown graphically in FIG. 1 as ageneral mapping or transformation K of a collection of coordinate pointsP₀ to a collection of target points P₁. Examples of thesetransformations for different embodiments of the present invention areshown in the chart of FIG. 13. Stated differently, FIG. 13 is a chart ofvarious embodiments for forward mapping and inverse mapping of acollection of source points P₀ to a collection of target points P₁.Further, row 1 of the chart in FIG. 13 is a general case of FIG. 1.

To determine the affine K matrix transformation from point sets P₀ toP₁:

-   -   a) KP₀=P₁ Original equation    -   b) KP₀P₀ ⁺=P₁P₀ ⁺ Right matrix multiply each side by the        pseudo-inverse of P₀    -   c) K(P₀P₀ ⁺)=P₁P₀ ⁺ where P₀P₀ ⁺ is effectively Identity, that        is P₀P₀ ⁺=I (with insignificant numerical error)    -   d) KI=P₁P₀ ⁺    -   e) K=P₁P₀ ⁺

Non-Limiting Definitions

“Actual image points” are a plurality of two-dimensional image points ina vector space that are printed on an imageable substrate and thenscanned by a scanner and made available to an imaging device. The actualimage points are used to compare to the reference image and/orcalibration points and/or other actual image points for see-throughalignment.

An “affine transformation” is a transform between two affine spaceswhich includes a linear transformation followed by a translation. Theuse of homogenous coordinates allows affine transformations to be easilyrepresented by a matrix K. The matrix K is in affine form and thereforecompatible with the standard Composite Transformation Matrix (CTM)format commonly used in computer graphics (as defined, for example, in.NET Framework 3.5) and Printer Description Languages (PDLs) for pointand image transformations (for example, in Portable Document Format byAdobe Systems, and PostScript, to name a few). As such, in order tocreate, enable, and apply affine transformations the individual datapoints in P must be converted to affine form: p_(n)={x_(n),y_(n),1}.

“Alignment errors” are deviations from image-to-image or image-to-sheetthat are caused by, for example sheet positioning error, input imagingdevice positional error, or shrinkage to the imageable substrate such asshrinkage to the paper or mechanical/optical/print head misalignments.Similarly, misaligned scan bars or mechanical paper alignment in thescanning workflow introduce errors in the saved and/or printed documentimage.

An “inverse” (or “backward”) mapping is where the set of points P₁ isassociated with the source vector space S and the set of points P₀ isassociated with the target vector space T. There is still a mappingbetween a source vector space to a target vector space, but the order ofpoint sets is reversed. For example, the matrix equation K₀₁=P₁P₀ ⁺represents a “forward” mapping, K: S→T, or more specifically K₀₁:[P₀]_(S)→[P₁]_(T). Note that P₀ is associated with the source vectorspace S, and P₁ is associated with the target vector space T withregards to direction of mapping or transformation. An “inverse” mappingis defined as: K₁₀: [P₁]_(S)→[P₀]_(T), Mathematically this isaccomplished in two ways. The first method is to take the matrix inverseof K₀₁, denoted K₀₁ ⁻¹. The second method is to calculate a new matrixby reversing point sets P₀ and P₁ and creating a new K mapping, K₁₀=P₀P₁⁺.

A “calibration image” is a type of reference image point set. Thecalibration image is a plurality of two-dimensional image points in avector space. These ideal or calibration image points can be stored in afile and/or printed on an ideal medium and scanned into the system. Theideal or calibration image points are the standard used to minimizedistortion and adjust alignment/placement of the image. Typicallycalibration image includes measureable positions that would be identicalto the printed/scanned output if no error was present.

A “customer image” is real-world image such as those on an imageablesubstrate. These include images created by the scan and/or print processincluding any errors and distortions caused by the imaging system. Adistinction is made between a calibration image used for registrationcharacterization or correction, and a customer image or imageablesubstrate. Once distortion and alignment errors derived from aregistration image are modeled, the correction inverse transformation iscalculated as part of a registration or calibration process andsubsequently applied to customer images during the RIP or scan processor both. For the Print Path one embodiment is where the inverse mappingpre-distorts and changes alignment such that when the actual forwardmapping inherent in the system or other scenario occurs the errorcancels out. Similarly, for post-RIP scenario or the Copy/Scan Path theresultant image is corrected post-RIP or post-scan, i.e., not“pre-distorted”.

“Control placement” refers to adjusting an imaging device based on totalerror, for example a scanner and printer whereby the scanner spatialerror and printer spatial error are each determined and the digitalprinter/copier or multi-function device is adjusted accordingly.

A “fiducial mark” refers to a mark defining a datum point or standard ofpositional reference used as a basis for calculation or measurement.

A “homogenous form” or “homogenous coordinates” are coordinates to allowaffine matrix transformations.

An “ideal medium” and “ideal media” refer to the media used as astandard to “control placement” of images by an imaging device (e.g., aprinter, digital copier or multifunction device). Alternatively, theterms “reference image” or “reference image points” or “ideal film” or“ideal virtual file” are “ideal media.”

An “image” refers to a spatial pattern of physical light comprised ofknown colors of the light spectrum which are visible by the human eye.When reduced to capture or rendering, the image generally comprises aplurality of colored pixels. A printed image (or image print) would be aphotograph, plot, chart, gloss mark, and the like, as are generallyknown. When an image is rendered to an electronic memory or storage, thevalues of the color pixels are generally stored in any of a variety ofknown formats such as BMP, JPEG, GIF, TIFF, or other formats employedfor storing image data on a storage media for subsequent retrieval.Received pixels of an input image are associated with a color valuedefined in terms of a color space, comprising typically 3 colorcoordinates or axes. Pixels of a received image may be converted to achrominance-luminance space such as CIELAB or YCbCr.

An “imaging device” or “imaging system” is any device capable ofcapturing image data as an image capture device and/or for reproductionand display of an image as an image output device. Examples of imagingdevice are printers, copiers, fax machines, scanners, camera, videodevices, and the like. One example imaging system is a multi-functiondocument reproduction system or multi-function machine (scan, copy, fax,and print).

An “image input device” is any device capable of capturing an image suchas a scanner or camera or fax machine and providing a signal of thecaptured image to an image output or storage device.

An “image output device” is any device capable of rendering an image.The collection of image output devices includes xerographic systems,multifunction devices, monitors and other displays, computerworkstations and servers, and the like. Image output devices receive asignal of an image and reduce that signal to a viewable form. An inkjetprinter is one image output device which receives a signal of an imageand renders the image into a viewable form by the visual integration ofcolored inks deposited onto an imageable substrate. An image outputdevice may incorporate some or all of the functionality of an imageinput device. An image output device includes printers andmulti-function machines (scan, copy, fax, and/or print).

An “imageable substrate” is a substrate such as paper, film, cardstock,photographic paper, Mylar, and other printable surfaces, upon which animage can be rendered.

A “linear transformation” is commonly defined as Ax=b, where A is atransformation matrix, x is a vector of source points, and b is thevector of mapped or transformed points. An inverse may be defined asx=A⁻¹b. Measured points typically contain a small amount of variation orerror. As a result, a noise term should be added to the linear modelAx=b. In these cases, a pseudo-inverse is used and denoted with a plussign as A⁺. The standard inverse may thus be defined as x=A⁺b. Note thatthe inverse is generally applied to the transformation matrix A, and notto the coordinate vectors x and b. In this invention we have two sets ofcorresponding spatial coordinate points: P relative to a source vectorspace S and P₁ relative to a target vector space T, and we seek todetermine the functional mapping, K, between them. In the first standardscenario we apply a pseudo-inverse to a transformation matrix. However,for determining the K mapping we now apply a pseudo-inverse to acollection of coordinate points. The unobvious difference between thestandard scenario and the approach used in this invention is that herewe will apply an inversion technique to measured, imprecise spatialaffine coordinate points versus a function or mapping. Conventionally,we may define this mapping in linear algebraic terms as KP₀=P₁ where itis understood that point sets are implicitly related to respectivevector spaces, where K becomes an affine matrix transformation, and theterm KP₀ involves a matrix multiplication.

A “mapping” or “transformation” K is used to represent or correctdistortion and alignment errors or other systemic differences betweentwo sets of points, P₀, P₁. such that KP₀=P₁ Alignment may also implyplacement of an object relative to another object (for example,image-to-image, image-to-sheet, or sheet-to -device).

“Positional information” refers to a location occupied by a geometricshape on a medium relative to a fiducial mark or coordinate point withinthe same image.

“Reference image points” are a plurality of two-dimensional image pointsin a vector space that includes calibration images.

“Registration” is used in document system to describe correct alignmentof images on sheets and involves mechanical and imaging adjustments toobtain the best possible results.

The terms “see-through” or “show-through” refer to a relative positionof a printed two-dimensional array on one side of a medium to theposition of a printed two-dimensional array on the other side of thesame imageable substrate.

A “spatial error” refers to the variation in positional informationbetween an ideal medium and a second (scanned, printed, or otherwisetransferred) medium. For example, averaging the collection of individualerrors for each point is computed to obtain the mean spatial error forthe entire imageable substrate.

A “two-dimensional array” or “2-dimensional array” or “2-D array” refersto any grouping of at least one geometric shape throughout the surfaceof an imageable substrate such as dots spanning a sheet of paper or in acomputer file.

Overview of Spatial Errors and Minimizing Distortion

The present system and method detects differences in positionalinformation associated with a two-dimensional array on reference imagepoints and a scan of the same two-dimensional array, so as to isolatespatial errors and minimize distortions caused by imaging systemsincluding scan errors and image output device errors. Differences inpositional information associated with a scan are detected and thereference image points of either calibration images and/or customerimages by deriving coordinate information from the scan and from theideal or reference image points. Several examples of mappings foralignment and reduction of distortion are now described. These examplesof mappings are applicable to both print and scan paths of an imagingsystem or imaging device. The mappings are CTM across varioussubsystems. Prototype with results of these mapping using Mathematicaare shown throughout and referenced in the accompanying Appendix.

Align-to-Reference

FIG. 2 illustrates a two-dimensional arrays as actual data points(actual in the sense this is what the imaging device is currentlyproducing) used for image registrations. FIG. 2 is has two-dimensionalarray 200 printed on an ideal medium 202 with coordinate space 250 asshown. In some embodiments, printer spatial error is determined by usinga calibration or reference image data points as part of an ideal medium,such as, a computer readable file or a printed sheet or film. Idealmedium 202 in this example is shown with a two-dimensional array 200that is defined by a grid of dots substantially covering the idealmedium 202. An example of the two-dimensional array 200 included on theideal medium 202 is shown in further detail in FIG. 2. For example, inone embodiment, hundreds of dots are arranged to substantially cover theideal medium 202. The two-dimensional array 200 also can includemultiple fiducial marks 216 that can be used for alignment duringanalysis. For example, the ideal medium 202 can include at least four(4) fiducial marks 216 or bulls-eyes for alignment of the ideal medium202.

FIG. 3 illustrates two-dimensional array 300 of reference image datapoints 350 used in image registrations. The reference image data pointsare the standard or gauge used to place the image.

The embodiment where the ideal medium 202 is scanned from a pre-printedsheet or film is now described. In another embodiment the referenceimage is accessed from a computer file. Turning to FIG. 4, uponprinting, ideal medium 202 is scanned using scanner 402. A location fora ideal medium 202 to be placed on a platen 404 of the scanner 402 ismarked so that the ideal medium 202 is placed at a substantiallyidentical location as the registration star mark 406. The ideal medium202 having the printed two-dimensional array 200 is then scanned. As aresult, the two-dimensional array 300 on the sheet 302 is at thesubstantially identical location on the scanner 402 as an ideal medium202 to be scanned. The scan of ideal medium 202 is then compared to thereference image of points of the calibration image. If this method isused, spatial errors and other distortions caused by imaging systemsincluding scan errors and image output device errors can be determined,not just printers operatively connected to a specific scanner combinedwith the architecture of FIG. 15 as described further below.

Using mathematical notation row 2 of FIG. 13 is a mapping betweenReference (R) and Actual (A) spaces. Aligning to Reference removes(minimizes) distortions and alignment issues. The forward mapping of acollection of Actual points A to a collection of reference points R,i.e., RA. Also shown is an inverse mapping along with correspondingmappings from AR and the inverse AR⁻¹. Here the system introduces errorRA, and the correction is AR. Stated differently, first the error isderived RA, and then the error is removed using AR. Mathematically,

K_(RA): [P₀]_(R)→[P₁]_(A) or K_(AR): [P₁]_(A)→[P₀]_(R)

Simplex and Duplex Align-to-Reference

In a duplex printed sheet it is desired and expected that images arealigned correctly on an imageable substrate. A common test is to print atest pattern on each side of a sheet such that with perfect alignmentthe registration marks will be aligned when the sheet is viewed is asee-through fashion (typically, holding the sheet to a light source sothat a customer can visually test alignment).

FIGS. 5-8 illustrate spatial errors and corrections to an actual imageback to reference images. All the orientations for FIGS. 2-3 and 5-13are oriented with the 250 X-Y axis kept in the same direction 202. It isimportant to note that other directions can be used and mappings betweendifferent coordinate spaces maybe used. Shown in FIG. 5 is an example ofa two-dimensional array 500 typically printed on an imageable substratesuch as a printed sheet (not shown). The two-dimensional array 500,includes a plurality of image points shown as geometric shapes 520 and540. In this example, two geometric shapes are shown a solid circle 520for the actual measured image points and a reference collection of imagepoints shown as an outline of a circle 540. It is important to note thatfor measurement purposes the exact size and shape and number of theimage points are not important as long as the spatial distance betweenthe centroids of the two image points 520 and 540 can be calculated.Although it has been shown that the number of points affects theaccuracy of the fit, testing has shown the fit is still good even with alimited collection of points. During control of image position,corrections are made to adjust for distortion and alignment betweenthese two geometric shapes 520 and 540 so that they align orsubstantially align 650 as shown in FIG. 6. This is known asAlign-to-Reference.

Displacement between spatial 2D points is represented as a displacementvector 530. The amount of registration error is therefore the magnitudeof the displacement vector at a particular location for a given pair ofpoints. This is the error for a single point. In another embodiment, theerror for an aggregate area across the 2D surface is determined usingany combination of total, mean, standard deviation, minimum and maximumerrors, histograms and other statistical analysis or functioncharacterizations on the collection of point errors.

In some embodiments, side 1 to side 2 (e.g., duplex) registration(see-through) are measured using a coordinate system that applies acommon reference to both sides of an ideal medium 202. In the case ofduplex with see-through alignment to a single reference, this process isrepeated for a second side as shown in FIG. 7. The example geometricshapes in this example are solid circle 720 for actual measured imagepoints and outline of a circle 740 for referenced points. In this duplexexample of Align-to-Reference there are two possible approaches to thechoice of reference sets of image points: Use a common set for both thefirst side and second side, or an individual collection of referencepoints for each side. A common collection of reference image pointsmeans the reference points 740 for the second side are the same asreference points 740 on the first side. The actual reference points 720are adjusted to substantially align and remove any distortion 650 toreference points 740 as shown in FIG. 6.

Mathematically, using mathematical notation row 3 of FIG. 13 is a Kmapping with a single reference image example to correct for see-throughalignment error. A reference image R containing point set P₀ is created.This image is printed to both the first side of the duplex sheet or A₀,and the same reference image R to second side of the sheet or A₁. A setof point P₁ is associated with first side and a set of point P₂ isassociated with second side.

From row 3 of FIG. 13, we have the following:

a) K_(RAD): [P₀]_(R)→[P₁]_(A0), or in matrix terms: K_(RA0)P₀=P₁ tomodel the error

b) K_(RA1): [P₀]_(R)→[P₂]_(A1), or in matrix terms: K_(RA1)P₀=P₂ tomodel the error

c) Solve for inverse correction mappings or transformations as definedearlier.

K_(RAD) ⁻¹: [P₁]_(A0)→[P₀]_(R) and K_(RA1): [P₂]_(A1)→[P₀]_(R)

d) Apply correction mappings or transformations as defined earlier.

Note that steps c and d generally apply to subsequent applications belowas well. For example this is useful for uncorrected see-throughalignment, forms and possibly HLC. Further, this is also useful whereone actual image is aligned to another actual image, but neither toreference.

In the case where there are individual sets of reference points, one foreach of the first side and the second side, the actual reference points720 are adjusted to substantially align 850 with the second sidereference image points 740 as shown in FIG. 8. More specifically, shownin FIG. 7 is an example of a two-dimensional array 700 typically printedon a second or back side of imageable substrate, where FIG. 5 representsthe array on the front or top side of the same imageable substrate. Asdescribed above for the first side in FIG. 5, the two-dimensional array700 of the second side, includes a plurality of image points shown asgeometric shapes 720 and 740. In this example, two geometric shapes areshown a solid circle 720 for the actual measured image points and areference collection of image points shown as an outline of a circle740. Mathematically, extending the notation of row 3 of FIG. 13, we havethe reference for the first side R₀ and reference for the second sideR₁:

a) K_(R0A0): [P₀]_(R0)→[P₁]_(A0), or in matrix terms: K_(R0A0)P₀=P₁ tomodel the error

b) K_(R1A1): [P₃]_(R1)→[P₂]_(A1), or in matrix terms: K_(R1A1)P₃=P₂ tomodel the error

c) Solve for inverse correction mappings or transformations as definedearlier.

K_(R0A0) ⁻¹: [P₁]_(A0)→[P₀]_(R0) and K_(R1A1) ⁻¹: [P₂]_(A1)→[P₃]_(R1)

d) Apply correction mappings or transformations as defined earlier.

Actual-to-Actual Duplex Alignment

Shown in FIGS. 9 and 10 are examples of a two-dimensional array 900 and1000 typically printed on each side of an imageable substrate such as aprinted sheet (not shown). In this case, there are is a first collectionof actual or measured image points 920 for the first side and a secondcollection of actual or measured image points 1020 for the second side.Stated differently the actual image points 920 on the first side arealigned to the actual image points on the second side 1020. To correctsee-through alignment in duplex images, one or both sets of actual imagepoints 920 and 1020 are adjusted to substantially align 1150 as shown inFIG. 11.

Aligning to a relatively perfect reference image(s) both removesdistortions and corrects placement. Another approach is to align oneuncorrected side to the other. Rather than remove distortions, thedistortions from one side are modeled such that the image on the secondside is modified to make the image align to the image on the first side.In this case, while distortions are still present they are essentiallyequivalent so that the distorted images appear visually to bewell-aligned when viewed see-through. At typical distortion levelsvisual inspection would appear to give good registration. It would alsoinvolve halving the registration transformation calculations. Thealgorithm is very fast, so from a computational perspective this wouldresult in only marginal productivity gains. A greater benefit includesreduced registration setup (typically manual) and measurement time,saving on labor effort and associated costs.

Mathematically, using mathematical notation row 4 of FIG. 13 is a Kmapping from the algorithm perspective the source space is actual side 0or A₀, and the target space is actual side 1 or A₁, K: A₀ A₁.Alternatively, a mapping in the opposite direction may be performed: K:A₁→A₀. Actual point sets derived from printing a registration image toeach side would be obtained. The K mappings:

a) K_(A0A1): [P₁]_(A0)→[P₂]_(A1), or in matrix terms: K_(A0A1)P₁=P₂

b) K_(A1A0): [P₂]_(A1)→[P₁]_(A0), or in matrix terms: K_(A1A0)P₂=P₁

Note that (b) is equivalent to one method described above for inverses.The other approach of using a matrix inverse on K will be effectivelythe same. It is important to note as shown in the Mathematica exampledescribed in the last section below, during implementation of thisalign-to-actual embodiment, the align-to-reference transformation of row3 of FIG. 13 and a similarity transformation is required as well. Suchtransforms are commonly used to map points in a single coordinate space.The usage here is to map a transformation between spaces. See: LinearAlgebra with Applications 2^(nd) Edition, by Otto Bretscher, Section 4.3Coordinates in a Linear Space.

Form Alignment Example

FIG. 12 illustrates spatial errors and corrections to a form used inimage registrations. This form can be preprinted in one embodiment, orin another embodiment electronic (e.g., a pre-printed form that isscanned). In certain cases these forms are also known as variable inputforms (VIP) where some of the information changes, such as a name, butthe body of the letter remains consistent. For example, credit card form1202 is shown with information printed on the form. Notice the type ofcredit card 1204 is checked but because of poor alignment the word Visais partially obscured. Likewise the text 1206 is shown not positioncorrection with respect to the lines. Also, the highlighting 1208 ismis-aligned to the corresponding line. Using the alignment to actualtransformation because forms have errors. The goal is to map theactual/distorted forms. In example case above, all these mis-alignmentproblems are minimized as further described below. A common printingapplication is print images onto pre-printed forms. The form may bemisaligned in the paper path, and/or the form image-to-sheet alignmentis off. Or the form may be distorted due to anomalies in the device itwas originally printed on. This is a different scenario from loading theform as a printable substrate in the final printing. In the embodimentwhere the form is a preprinted form as opposed to an electronicallystored form, the form may experience shrinkage as part of the fusingprocess, and so forth. Recall there are two possible sources ofshrinkage with a pre-printed form. The first source of shrinkage is dueto original fusing and the second source of shrinkage is due to finalfusing.

Mathematically, using mathematical notation row 5 of FIG. 13 is a Kmapping, the form becomes the source space F (which is a kind of actualA₀) and the actual point set derived from printing a registrationreference image to a sheet side A₁ and both are used to define themapping K_(FA1). This is simply a special case of above ofActual-to-Actual alignment where the form F was printed previously. Toobtain form registration point sets either the form maker would includethis or in certain cases it could be derived via the form itself. Thecustomer image to be printed onto the form is manipulated so as to fitonto the imperfect, distorted form (e.g., the form has skew, shift, andstretching error that will be adapted to). The K mappings would beeither (a) or (b):

a) K_(FA1): [P₁]_(F)→[P₂]_(A1), or in matrix terms: K_(FA1)P₁=P₀

b) K_(A1F): [P₂]_(A1)→[P₁]_(F) or in matrix terms: K_(A1F)P₂=P₁

Highlight, Layer or Engine Alignment

This approach is very similar to the Form Alignment Example above,however instead of alignment to form, a highlight color, color layer ormarking engine alignment in an imaging system (comprising multipleimaging subsystems and/or devices) is now being aligned and corrected.This involves overlaying one image on top of another. Registrationerrors are unusually present because of imaging or mechanical alignmentanomalies. Typically multiple marking engines are used in a sequentialfashion where each engine marks/overlays an image. As in the earlierexamples, images may all be aligned to a common reference, oralternatively, to an actual image produced by one of the markingengines. As such this is a special application of reference-actual oractual-actual distortion and alignment correction on a per side basis.Printing could be simplex or duplex, but related images are typicallynot see-through but rather from disparate printing engines in the printpath. Of course this does not mean see-through alignment for duplexscenarios is no longer important. Any number of marking engines may bechained together (only 2 are shown in FIG. 13). Further, any number ofpasses for one or more engines is also within the true scope and spiritof the present invention.

For Highlight Color (HLC) and similar applications typically multipleengines mark multiple image Layers onto a sheet. Transformations aremodeled as above and can use either the Align-to-Reference orAlign-to-Actual transformations (corrected or uncorrected). Here onlyAlign-to-Actual is shown (e.g., align all layers to first layer markedon first engine in a sequence of engines). An Align-to-Referencealternative would follow as above where all actual images for eachengine/layer are mapped back to a common reference and are thus bothaligned across engines and corrected to reference.

As before points P are relative to spaces R or A, but are now qualifiedrelative to which marking engine E is used. Following convention,another collection of nesting brackets are used. For example, the pointsP_(n) are marked as an actual image A_(n) on engine E_(n) would be:[[P_(n)]_(An)]_(En).

Mathematically, using mathematical notation row 6 of FIG. 13 is a Kforward mapping with an engine denoted E_(n),:

a) K_(A0A1):[[P₀]_(A0)]_(E0)→[[P₁]_(A1)]_(E1), or in matrix terms:KR_(A0A1)P_(0A0E0)=P_(1A1E1) (Align-to-Reference)

b) K_(A1A0): [[P₁]_(A1)]_(E1)→[[P₀]_(A0)]_(E0) or in matrix terms:K_(A1A0)P_(1A1E1)=P₂ (Align-to-Actual)

Note the additional bracketing included to show that point sets arerelative to reference or actual spaces, which in turn are relative to aparticular engine. Similar K mappings are possible and straightforwardfor duplex side 2 using A₁.

High Level Flow Diagram

FIG. 14 is a flow diagram for correcting the errors in FIGS. 5-13according to an embodiment of the present invention. The process beginsat step 1402 and immediately proceeds to step 1404 where a sourcecollection of image points P₀ in a source vector space is received. Alsoreceived is a target of image points P₁ in a target vector space. Thesesource collections of points are the domain two dimensional (2D) spatialcoordinate points and the target collection of points P₁ are the mappedco-domain.

Next is step 1406, the source collection of 2D image points and thetarget collection of 2D image points are converted into a homogenousform to create or apply affine matrix transformations.

In step 1408, the process solves for transformation K, where in matrixform K P₀=P₁ by performing the following:

-   -   Take pseudo-inverse of P₀, such that, P₀→P₀ ⁺    -   Right multiply both sides by P₀ ⁺, such that, KP₀P₀ ⁺=P₁P₀ ⁺;        and    -   Have P₀P₀ ⁺ reduce to the Identity Matrix “I”, such that,        KI=P₁P₀ ⁺, therefore K=P₁P₀ ⁺.

In step 1410, the inverse mapping K⁻¹ is used to map the targetcollection of homogeneous coordinate points to points in the domain ororiginal source coordinate space to verify the goodness of fit bycomparing to original points. Recall that the pseudo-inverse inconjunction with matrix algebra produces an optimized fit. If thecoordinate point information in each space and mapping/transformationwere completely accurate the results would be equivalent to using normalmatrix algebra. That is, the mapping/transformation in matrix form wasinvertible using matrix inversion. Further, the points in the co-domainor target space are mapped with no significant error. Implicit in theuse of this method is a more robust forward/inverse mapping assumingsome variability in the mapped coordinate points which disables theability to use a standard matrix inverse. Matrix inversion ofhomogeneous coordinate points is not meaningful in this context outsideof enabling subsequent matrix algebra that exposes the K mappings.Mappings maybe applied in step 1412 during image creation and/orafterwards (e.g., Post-RIP).

The flow may repeat if there is another space to map, such as a secondcolor or print head, or side of imageable substrate. In step 1414, atest is made to determine if there is another space. In the event thereare no other spaces to map, the flow ends in step 1420. In the eventcoordinate points for another space are available, the process continuesto step 1416 to test if another collection of coordinate points will beused. If not the flow continues up back to step 1406. In the eventanother collection of coordinate points will be used, the flow continuesto step 1418 to set P₁ to another collection of 2D image points in aanother vector space, that is different from the source and targetspaces, for another space before continuing to step 1406.

System Architecture and Application of CTM to Various Subsystems

More specifically, the transform or mapping matrix K described above canbe thought of a CTM matrix i.e., a composite of rotation, scaling,translation, and shear. It is an affine matrix in computer graphicsform. As such it is readily consumed by computer graphics-oriented orPrinter Device Language (PDL) products and software libraries. Examplesinclude Postscript, graphics accelerator cards, and any computergraphics package such as OpenGL, Windows.NET, and Java. Typicalregistration setup routines require discrete values for rotation,scaling, translation and possibly shear. Techniques previouslydiscovered and developed may be used to decompose a given CTM matrixinto rotation, scaling, translation and shear values. Furtherinformation, on the mathematical correction performed by the presentinvention are in CTM form and therefore readily consumable by e.g.,Postscript, image processing, and computer graphics cards, and can bedecomposed into discrete operations. This decomposition is described infour U.S. patent application Ser. Nos. 12/338,260, 12/338,300,12/339,148 and 12/338,318 (Attorney docket numbers 20061977-US-NP,20061982-US-NP, 20070602-US-NP, 20061983-US-NP) all filed Dec. 18, 2008,each entitled “Method And System For Utilizing Transformation In ProcessRasterized Image Data”, and commonly assigned herewith to XeroxCorporation and the teachings of each incorporated herein by referencein its entirety including any continuations, and continuations-in-partsthereof describing shear. As important is the order of decompositionresults because operations are non-commutative (e.g., a rotationfollowed by a scaling will give different results than a scalingfollowed by a rotation for same values of rotation degree and scalingfactors). For mechanical and xerographic registration operations theorder is specific and device-dependent, so the decomposition willtypically require reordering of transformations so that they are alignedwith real behavior of the system (less of a constraint for purelygraphical operations). Further, registration requires handling smallangle rotations (versus orthogonal {0, 90, 180, 270} degrees) and shearwhich the decomposition algorithms are able to provide. This presentmethod and system expands on the inventors previously developedalgorithms to obtain the decomposition as required by registration.

The CTM above allows for forward mapping, for example fromReference-to-Actual, and inverse mapping from Actual-to-Reference.Decomposition may be applied to both directions. Decomposing the forwardtransformation yields insights into what transpired to produce theobserved distorted result. Note that this depends upon the uniqueness ofthe decomposition step, and appropriate reordering to mirror actualworkflow. Decomposition of the inverse transformation, fromActual-to-Reference, produces the discrete values needed for mechanicaland xerographic registration setup. For the example shown in theattached, alignment prior to marking involves rotation and translation,and the marking/fusing step causes scaling/shear distortions. Analternative would be to align via translation first, then the rotation,but since the fusing step is last scaling/shear distortions aretypically last unless the translation step is also done in thexerographic subsystem via imaging vs. mechanical shifting. Thereordering of the decomposed matrices must reflect the actual processingorder inherent in a particular product. Note that the execution locationof each of the decomposed operations is a design choice and the fullcollection of decomposed operations may be distributed.

It is important to note that there are two sources of CTMs. One sourceof CTMs, which is an embodiment of the present invention, is used tomodel the imaging device due to device imperfections. A second commonsource of CTMs is discrete graphics operations requested by the remoteuser or printer operator. Theses two kinds of CTMs can be combined usingthe present invention.

FIG. 15 is a system diagram of the imaging device used to carry out themethod of FIG. 14, according to an embodiment hereof, illustrating anexemplary image path for printing, scanning, copying or a combination ofeach of these operations in an imaging device 1500. Distortions areminimized and spatial errors are corrected across possibly differentsubsystems within an imaging device, such as a printer, multi-functionmachine, scanner, fax, copier or other system. The manipulations includethe image transformations of translation, rotation, scaling, and shear.

The imaging device 1500 in accordance with one or more aspects of thepresent disclosure, comprises one or more Raster Image Processor(s)(RIPs) and/or scan processor(s) 1504 associated with an image buffermanager 1506 communicatively coupled to a print engine(s) 1550 thatprint images on a printable media or printable substrate 1560 introducedthereto. For scanning or copying or faxing operations, the job may notbe printed but rather put in an imaging buffer manager 1506 for lateruse such as e-mail, local or remote storage, and more non-printingfunctions. The term “scanning” is used in this description to meanscanning, copying or faxing.

The imaging device includes a digital front end 1502 (DFE) havingcalculation control 1530 and a transformation data in a CompositeTransformation Matrix (CTM) database 1534 with decompose/reorder module1532 for applying transformation on images over one or more subsystemsof RIPs and/or scan processor(s) 1504, one or more image processor(s)1520 and print engine(s) 1550 according to the present invention.Although the image processor(s) 1520 are shown outside the DFE 1502, itin this embodiment, in other embodiments the image processor(s) 1520 areinside the DFE 1502. The CTM database 1534 includes data to handletranslation, rotation, scaling, and shear. The DFE 1502 may includeadditional RIP instances (not shown), such as a PostScript RIP, a PCLRIP, etc., wherein each RIP instance is operatively coupled withcorresponding multiple imagers. Furthermore, a single print job may beprocessed by two or more RIP instances of the same type (e.g., pageparallel RIP). The print engine(s) 1550 may include separate color andmonochrome engines that work cooperatively under the control of morethan one image processor(s) 1520. For example, many times differentimage processors are used to perform separate tasks, e.g.,translation/rotate and another to perform compression, although not arequirement of the disclosure. In another possible implementation, forexample, two or more color imagers could be provided with a singlecomponent RIP and/or scan processor(s) 1504 in a DFE 1502, where one ofthe imagers is associated with a print engine having a lower print costthan a print engine associated with the other imager. Still anotherpossible example includes two or more monochrome imagers associated withprint engines having different associated print costs. The imagingdevice 1500, moreover, can have a modular architecture that allows printengine(s) 1550 to be interchanged with other print engines, wherein someengines may be adapted to produce color printed images while others maybe limited to monochrome imaging. The DFE 1502 includes an image buffermanager 1506 for managing output from the RIPs and/or scan processor(s)1504 being fed into the print engine(s) 1550. Although the imageprocessor(s) 1520 is shown as part of the imaging device 1500, it isimportant to note that the image processor(s) 1520 may be in multipleplaces within the image path and/or divided into more than one imageprocessor. Image processor(s) may be utilized, for example, to aid inthe rendering part of RIP (in-RIP), post-RIP when reprinting, and in theprint engine(s) 1550.

The CTM database 1534 in one embodiment stores calibration informationto different imageable substrates e.g. different sheet sizes, differentsheet weight, and other system/printer/scanner/copier/multifunctiondevice variables. For example, there would be different CTMs for 11×17with two different weights. Calibration for different configurations andvariables are associated with a given CTM. Stated differently, the useof the CTM database 1534 provides associated information and metadatadescribing the information in a database record for a CTM. Suppose arun-time scenario a imaging job comes in for a request for givenimageable substrate, the image system 1500 is configured based on theserequirements and the corresponding CTM is retrieved from the CTMdatabase 1534 and configures the incoming job to run it in Postscript.The CTM can be applied at different subsystems in the imaging system1500.

The print engine(s) 1550 may be any device or marking apparatus forapplying an image from the DFE 1502 to printable substrate (print media)1560 such as a physical sheet of paper, plastic, or other suitablephysical media substrate for images, whether precut or web fed. Theprint engine(s) 1550 generally includes hardware elements employed inthe creation of desired images by xerographic processes and may alsoinclude ink-jet printers, such as solid ink printers, thermal headprinters that are used in conjunction with heat sensitive paper, andother devices capable of printing an image on a printable media 1560.

The DFE 1502 can be any suitable hardware, software, or combinationsthereof, whether a unitary system or a plurality of systems implementingthe front end functionality in distributed form to provide an interfacebetween submitting host 1510 providing incoming image job(s) 1512 andthe print engine(s) 1550 in the print path or scan processors 1504 inthe scan path. In one embodiment, the print path for the imaging device1500 can be any form of commercial printing apparatus, copier, printer,scanner, fax machine, or any other printing system with one or moreprint engine(s) 1550 by which visual images, graphics, text, etc. areprinted on a page or other printable medium 1560, including xerographic,electro photographic, and other types of printing technology, whereinsuch components are not specifically illustrated to avoid obscuring thevarious alternate imaging features of the present disclosure.

FIG. 15 includes a queue 1508 having various hardware memory, diskdrives, or other storage apparatus by which one or more incomingprint/scan/copy/fax, i.e., MFD jobs 1512 can be received from a computeror other host 1510 and stored, in whole or in part, for processing by aRIPs and/or scan processor(s) 1504. The scan or copy can be local orremote to imaging device 1500. The scan/copy typically produces a PDFfile or an image file, such as TIFF. The print path can consume PDFsthat get RIPped into images, including TIFF. For example, the image job1512 may be generically PDL or specifically PDF in the case of printing.Likewise, in the case of scanning or copying, the image job 1512 may bePDF or TIFF. In one embodiment, the RIPs and/or scan processor(s) 1504operates in concert with the queue 1508 to process incoming print jobs1512 to thereby create RIPped or scanned objects, which are stored in animage buffer manager 1506 of the DFE 1502. Calculation control 1530 inassociation with Composite Transformation Matrix (CTM) database 1534 anddecompose/reorder module 1532 provides image operations of translation,rotation, scaling and shear using one or more CTMs at various subsystemswithin imaging device 1500. Some subsystems such as the RIPs and/orimage processor(s) 1504 can consume CTMs directly and do not need toconsume discrete values after decompose/reorder. However, the printengine(s) 1550 as part of the print path of imaging device 1500typically cannot consume CTMs directly and must have these CTMs brokendown through decompose/reorder module 1532 into discrete values.

In one embodiment, objects which are scans, faxes, or copies are savedto a computer readable file and processed to remove distortions andmisalignments. In another embodiment, imaging jobs commonlyRIPped/scanned into the image buffer manager 1506 are processed by imageprocessor(s) 1520 to produce raster page images for use by printengine(s) 1550. In the print engine, a printable substrate registrationsubsystem 1552 aligns the printable substrate 1560 for image formationon xerographic subsystem(s) 1554. In one embodiment, this distortionremoval and alignment may be corrected using CTM database 1534 entriesthat have been decomposed and reordered 1532 and applied to either thepaper registration subsystem(s) 1552 or the xerographic subsystem(s)1554 or both. For example, rotation/skew and/or translation/shift wouldtypically be for printable substrate alignment such as paper alignmenti.e., squaring up the paper in the printable registration subsystem1552. Whereas in the case of scaling and/or shear, these operationswould probably be handled via imaging techniques employed at thexerographic subsystem(s) 1554. However, it is important to note thatthese image transformations can be done in other subsystems within theimaging device 1500 as well. Registrations in imaging devices such asprinting systems are described with reference to FIG. 15.

Imaging device 1500 can receive job programming 1516 at the userapplication level. For example, a job may include rotating an image by90, 180, or 270 degrees, scaling up or down the image, ortranslating/shifting the image in one or more directions. Jobprogramming 1516 is handled by RIPs and/or scan processor(s) 1504 or atimage processor(s) 1520. For example, during or after RIP or scan atranslation and/or rotation is performed according to the userapplication in order to accommodate a printable substrate 1560 with3-holes punched along one side.

It is important to note that the present invention overcomes a commonproblem of image processing cards in a document imaging device notworking well with small rotation angles that are smaller than 90degrees, e.g., 1.6 milliradians rotation angle. The present inventionenables “small angle rotations” typically adjusted in the registrationsubsystem(s) along with shear corrections. Alternatively, morepowerful/flexible image processors or computer graphics cards (uncommonin a typical document imaging device) may also handle small-anglerotations and shear.

In another embodiment, job programming 1516 and CTMs from CTM database1532 under calculation control 1530 are combined at RIPs and/or scanprocessor(s) 1504 and/or combined at the image processor(s) 1520 or aportion of the transformation applied at both the RIPs and/or scanprocessor(s) 1504 and image processor 1520. The process ofdecomposition/reordering image transformations 1532 using CTM has beenreferenced above. Using the architecture of the present invention, it ispossible to combine several different sources of adjustment to theimaging device 1500. This combination of adjustments can be made in boththe print path and the scan path. For example in the print path,adjustments can be made by both the user applications specified by jobprograms 1516 and the site policies 1514. This combination ofadjustments can be further combined with compensation made to adjust theprint engine(s) 1550. Likewise, in the scan path, adjustments can bemade by both the user applications specified by job programs 1516 andthe site policies 1514 to be combined with compensations made to adjustthe scanned image to remove scanner inherent distortions/misalignments.

In one embodiment an automatic calibration routine is run based uponsite policies. For example, a calibration is automatically run inresponse to determining that the tolerances for errors and distortion ofthe machine 1550 are outside a given site policy.

Adjustments can be further combined to adjust the scan engine(s) (notshown). The present system and method permits adjustments to be made invarious places. In one embodiment, the compensation/adjustments aremade, wherever they occur, in order to correct for inherent systemicerrors in the device. Further these adjustments/compensation can be apure correction, applied e.g., at RIP-time, dynamically for each imagegenerated. In another embodiment these adjustments/compensations couldbe more static as controlled by the “machine setup” for printablesubstrate registration subsystem(s) 1552 and xerographic subsystem(s)1554. For example, the job programming specifies a 90 degree rotationand calculation control 1530 compensates for a 0.5 degree rotationalerror in the print engine(s) 1550. These are two transformations of 90degrees and 0.5 degrees. Transformations can be combined or compositedthen decomposed and the decomposed operations can be distributed across4 regions of device 1500 as desirable. These four distinct regions are:i) the RIP(s) and/or ii) scan processor(s) 1504, iii) the imageprocessor(s) 1520; and/or iv) the print engine(s) 1550. Further, theprint engine(s) 1550 broadly has at least two distinct subsystems wherethese transformations can be applied individually or together i.e., thepaper (imageable substrate) registration subsystem(s) 1554 andxerographic subsystem(s) 1552 in the print engine(s) 1550. Applying thetransformation at RIPs and/or scan processor(s) 1504 allows printchanges to be addressed for a specific imaging device 1500. These printchanges many times are independent of image quality problems, which isdesirable. On the other hand, applying the transformation at RIPs and/orscan processor(s) 1504 or scan time results in the machine-specificcorrections/transformations to become part of the image i.e., “bakedinto the image” independent of image quality problems. Therefore,transformations applied during RIP are no longer independent of theprint engine; rather these transformations are dependent on thecalibration to the specific engine.

Further, applying the transformation at image processor(s) 1520 allowsprint quality issues to be addressed across various imaging device i.e.,the correction transformation is no longer device dependent to theoriginal device or an outdated device state (e.g., drift since machineregistration was calibrated). For example, a correction that is not“baked into the image” could be reprinted from storage to anotherimaging device that would apply its own device dependent correction toremove the errors on that remote device.

Still, further, applying at the print engine(s) 1550 allows thealignment issues such as those due to paper quality, types of printmedia for the printable substrate 1560, color overlays, one and two-sideprinting alignment, see-through through alignment, align to form,aligning images/paper to be handled very precisely. Printer engine 1550adjustments allow for corrections to be made possible in a multi-engineenvironment e.g., HLC—highlight color and more.

It should be understood that the architecture described in FIG. 15, withcalculation control 1530 and CTM database 1534 along withdecompose/reorder module 1532 allows site policies 1514, job programming1516 and image quality corrections to be combined and applied togetheror independently over one or more subsystems of RIP(s) and/or scanprocessor(s) 1504, image processor (s) 1520 and print engine(s) 1550according to the system and method hereof.

In another embodiment in which the imaging device 1500 has limitedcomputational capacity, such as a multifunction device (copy, scan, fax,printer), the error correction and alignment of imaging device 1500 isperformed on a separate computer that is external to imaging device1500. In this embodiment, the error of the imaging device 1500 iscaptured as part of a registration setup by a customer or a technician.This error is gathered by the personal computer for analysis andcomputation of the CTMs. The resulting CTMs are then transferred fromthe personal computer to the imaging device 1500.

Prototype Using Mathematica

FIGS. 16-24 are a series of histogram plots computed by mathematicalmodel the flow of FIG. 14 on the system of FIG. 15, according to anembodiment of the present system and method. Note that mapping pointsresults in a new set of points. As a simplification for the histograms anew convention is introduced. Points are explicitly defined relative toa particular space, for example: [P₂]_(A1). For or the histograms,rather than show a new set of points (e.g. P₃) the space the points aremapped to is changed instead. This implicit mapping is conceptuallysimpler. For example, mapping P₂ from A₁ space to A₀ space would berepresented as follows: [P₂]_(A1)→[P₂]_(A0). For programming reasons newpoint variables are needed and defined in the actual prototype code.Further note the use of absolute value symbols (e.g., “|x|”) surroundingthe equations to denote vector magnitude. Since P is a set of points,the absolute value in this context means finding the vector displacementmagnitude for each point in the collection. This model was implementedin Mathematica by Wolfram Research in appendix entitled “AppendixMathematica Prototype”.

Non-Limiting Examples

It should be understood that the flow diagrams depicted herein areillustrative. One or more of the operations illustrated in any of theflow diagrams may be performed in a differing order. Other operations,for example, may be added, and operations may be modified, enhanced,condensed, integrated, or consolidated. Variations thereof areenvisioned and are intended to fall within the scope of the appendedclaims.

It should also be understood that the method described in the flowchartsprovided herewith can be implemented on a special purpose computer, amicro-processor or micro-controller, an ASIC or other integratedcircuit, a DSP, an electronic circuit such as a discrete elementcircuit, a programmable device such as a PLD, PLA, FPGA, PAL, PDA, andthe like. In general, any device capable of implementing a finite statemachine that is in turn capable of implementing one or more elements ofthe flow diagrams provided herewith, or portions thereof, can be used.Portions of the flow diagrams may also be implemented partially or fullyin hardware in conjunction with machine executable instructions.

Furthermore, the flow diagrams hereof may be partially or fullyimplemented in software using object or object-oriented softwaredevelopment environments that provide portable source code that can beused on a variety of computer, workstation, server, network, or otherhardware platforms. One or more of the capabilities hereof can beemulated in a virtual environment as provided by an operating system,leverage specialized programs or leverage off-the-shelf computergraphics software such as that in Windows, Java, or from a server orhardware accelerator or other image processing devices.

The teachings hereof can be implemented in hardware or software usingany known or later developed systems, structures, devices, and/orsoftware by those skilled in the applicable art without undueexperimentation from the functional description provided herein with ageneral knowledge of the relevant arts.

Moreover, the methods hereof may be readily implemented as softwareexecuted on a programmed general purpose computer, a special purposecomputer, a microprocessor, or the like. In this case, the methodshereof can be implemented as a routine embedded on a personal computeror as a resource residing on a server or workstation, such as a routineembedded in a plug-in, a photocopier, a driver, a scanner, aphotographic system, a xerographic device, or the like. The methodsprovided herein can also be implemented by physical incorporation intoan image processing or color management system.

One or more aspects of the methods described herein are intended to beincorporated in an article of manufacture, including one or morecomputer program products, having computer usable or machine readablemedia. For purposes hereof, a computer usable or machine readable mediais a medium containing machine readable instructions, for example, afloppy disk, a hard-drive, memory, CD-ROM, DVD, tape, cassette, or otherdigital or analog media, or the like, which is capable of havingembodied thereon a computer readable program, one or more logicalinstructions, or other machine executable codes or commands thatimplement and facilitate the function, capability, and methodologiesdescribed herein.

Furthermore, the article of manufacture may be included on at least onestorage device readable by a machine architecture or other xerographicor image processing system embodying executable program instructionscapable of performing the methodology described in the flow diagrams.Additionally, the article of manufacture may be included as part of axerographic system, an operating system, a plug-in, or may be shipped,sold, leased, or otherwise provided separately either alone or as partof an add-on, update, upgrade, or product suite.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Variouspresently unforeseen or unanticipated alternatives, modifications,variations, or improvements therein may become apparent and/orsubsequently made by those skilled in the art which are also intended tobe encompassed by the following claims. Accordingly, the embodiments setforth above are considered to be illustrative and not limiting. Variouschanges to the above-described embodiments may be made without departingfrom the spirit and scope of the invention. The teachings of any printedpublications including patents and patent applications are eachseparately hereby incorporated by reference in their entirety.

1. A computer-implemented method to control placement of an image on animaging device, the method comprising: receiving a source collection ofa plurality of two-dimensional image points in a source vector space fora source image and a target collection of a plurality of two-dimensionalimage points in a target vector space for a target image, wherein thesource collection of the plurality of two-dimensional image points andthe target collection of the plurality of two-dimensional image pointsare different due to errors in the imaging device; converting the sourcecollection of two-dimensional image points and the target collection oftwo-dimensional image points into a homogenous form to enable and applyaffine matrix transformations; solving for a matrix transformation tomap the target collection of the plurality of two-dimensional imagepoints to the source collection of the plurality of two-dimensionalimage points, wherein the matrix transformation is one of an inversematrix transformation, and a reverse mapping; and adjusting, using thematrix transformation, at least one of distortion and alignment of thetarget image to control placement of the target image in an imagingdevice.
 2. A computer-implemented method to control placement of animage on an imaging device, the method comprising: receiving a sourcecollection of a plurality of two-dimensional image points in a sourcevector space S for a source image and a target collection of a pluralityof two-dimensional image points in a target vector space T for a targetimage, wherein the source collection of the plurality of two-dimensionalimage points and the target collection of the plurality oftwo-dimensional image points are different due to errors in a system;converting the source collection of two-dimensional image points and thetarget collection of two-dimensional image points into a homogenous formto enable and apply affine matrix transformations; solving for a matrixtransformation to map the source collection of the plurality oftwo-dimensional image points to the target collection of the pluralityof two-dimensional image points; and using the matrix transformation toadjust at least one of distortion and alignment of the target image inan imaging device.
 3. The computer-implemented method of claim 2,wherein the source vector space and the target vector space areassociated with a first side of an imageable substrate and the sourcevector space is for a reference image, the method further comprising:receiving a third collection of a plurality of two-dimensional imagepoints in a third vector space for a third image, representing a targetimage associated with a second side of the imageable substrate;converting the third collection of two-dimensional image points into ahomogenous form to enable and apply affine matrix transformation;solving for a matrix transformation to map the source collection of theplurality of two-dimensional image points to the third collection of theplurality of two-dimensional image points; and using the matrixtransformation to adjust at least one of distortion and alignment of thethird image in an imaging device.
 4. The computer-implemented method ofclaim 2, wherein the target collection of the plurality oftwo-dimensional image points represents a customer image, and the sourcecollection of the plurality of two-dimensional image points represents areference image.
 5. The computer-implemented method of claim 4, whereinthe source image is a preprinted form.
 6. The computer-implementedmethod of claim 4, wherein the source image is associated to at leastone of a first layer and a first marking engine printed by the imagingdevice and the target image is associated with at least one of a secondlayer and at least one of the first marking engine and a second markingengine printed by the imaging device.
 7. The computer-implemented methodof claim 2, wherein the source vector space and the target vector spaceare associated with a first side of an imageable substrate and thesource vector space is for a reference image associated with a firstside, and further comprising: receiving a third collection of aplurality of two-dimensional image points in a third vector space for athird image representing a target image associated with a second sideand receiving a fourth collection of a plurality of two-dimensionalimage points in a fourth vector space for a fourth image representing asource image associated with a second side; converting the thirdcollection and fourth collection of two-dimensional image points into ahomogenous form to enable and apply affine matrix transformation;solving for a matrix transformation to map the fourth collection of theplurality of two-dimensional image points to the third collection of theplurality of two-dimensional image points; and using the matrixtransformation to adjust at least one of distortion and alignment of thethird image in an imaging device.
 8. The computer-implemented method ofclaim 2, wherein the source collection of the plurality oftwo-dimensional image points represents actual image points associatedwith a first side of an imageable substrate for see-through alignmentand the target collection of the plurality of two-dimensional imagepoints represents target image points associated with a second side ofan imageable substrate.
 9. The computer-implemented method of claim 2,wherein the source collection of the plurality of two-dimensional imagepoints comprises a source grid of at least one geometric shapesubstantially covering an ideal medium.
 10. The computer-implementedmethod of claim 9, wherein the target collection of the plurality oftwo-dimensional image points comprises at least one geometric shapesubstantially similar to the source grid of geometric shapes.
 11. Thecomputer-implemented method of claim 2, wherein the receiving the targetcollection of a plurality of two-dimensional registration image pointsincludes receiving an image with associated distortion and/ormis-alignment of the imaging medium by an image capture device.
 12. Thecomputer-implemented method of claim 2, wherein the source collection P₀of the plurality of two-dimensional image points represents the sourcevector space, the target collection of the plurality of two-dimensionalimage points P₁ represents the target actual image space, the matrixtransformation comprises KS=T, the inverse matrix comprises apseudo-inverse of the source collection of two-dimensional image pointsP₀ ⁺ in the source vector space, and the mapping comprises K=P₁P₀ ⁺. 13.The computer-implemented method of claim 12, wherein the transformationK is solved by taking KS=T by: taking a pseudo Inverse of P₀, such that,P₀→P₀ ⁺; multiply both sides by P₀ ⁺, such that, KP₀P₀ ⁺=P₁P₀ ⁺; andreducing P₀P₀ ⁺ to an identity matrix I, with KI=P₁P₀ ⁺, such thatK=P₁P₀ ⁺.
 14. A system to control placement of an image on an imagingdevice, the system comprising: a memory; a storage medium for storingdata; and a processor in communication with said storage medium and saidmemory, said processor executing machine readable instructions forperforming the method of: receiving a source collection of a pluralityof two-dimensional image points in a source vector space S for a sourceimage and a target collection of a plurality of two-dimensional imagepoints in a target vector space T for a target image, wherein the sourcecollection of the plurality of two-dimensional image points and thetarget collection of the plurality of two-dimensional image points aredifferent due to errors in a system; converting the source collection oftwo-dimensional image points and the target collection oftwo-dimensional image points into a homogenous form to enable and applyaffine matrix transformations; solving for a matrix transformation tomap the source collection of the plurality of two-dimensional imagepoints to the target collection of the plurality of two-dimensionalimage points; and using the matrix transformation to adjust at least oneof distortion and alignment of the target image in an imaging device.15. The system of claim 14, wherein the source vector space and thetarget vector space are associated with a first side of an imageablesubstrate and the source vector space is for a reference image, themethod further comprising: receiving a third collection of a pluralityof two-dimensional image points in a third vector space for a thirdimage, representing a target image associated with a second side of theimageable substrate; converting the third collection of two-dimensionalimage points into a homogenous form to enable and apply affine matrixtransformation; solving for a matrix transformation to map the sourcecollection of the plurality of two-dimensional image points to the thirdcollection of the plurality of two-dimensional image points; and usingthe matrix transformation to adjust at least one of distortion andalignment of the third image in an imaging device.
 16. The system ofclaim 14, wherein the target collection of the plurality oftwo-dimensional image points represents a customer image, and the sourcecollection of the plurality of two-dimensional image points represents areference image.
 17. The system of claim 16, wherein the source image isa preprinted form.
 18. The system of claim 16, wherein the source imageis associated to at least one of a first layer and a first markingengine printed by the imaging device and the target image is associatedwith at least one of a second layer and a second marking engine printedby the imaging device.
 19. The system of claim 14, wherein the sourcevector space and the target vector space are associated with a firstside of an imageable substrate and the source vector space is for areference image associated with a first side, and further comprising:receiving a third collection of a plurality of two-dimensional imagepoints in a third vector space for a third image representing a targetimage associated with a second side and receiving a fourth collection ofa plurality of two-dimensional image points in a fourth vector space fora fourth image representing a source image associated with a secondside; converting the third collection and fourth collection oftwo-dimensional image points into a homogenous form to enable and applyaffine matrix transformation; solving for a matrix transformation to mapthe fourth collection of the plurality of two-dimensional image pointsto the third collection of the plurality of two-dimensional imagepoints; and using the matrix transformation to adjust at least one ofdistortion and alignment of the third image in an imaging device. 20.The system of claim 14, wherein the source collection of the pluralityof two-dimensional image points represents actual image pointsassociated with a first side of an imageable substrate for see-throughalignment and the target collection of the plurality of two-dimensionalimage points represents target image points associated with a secondside of an imageable substrate.